Firstly, a technology of a conventional photographing apparatus is described. Herein, as an example of a photographing apparatus, a monitoring camera apparatus is described.
Recently, a technology related to various monitoring camera apparatuses has been proposed. In particular, in a monitoring camera apparatus for performing a monitoring operation day and night, a technology of disposing an infrared-light cut filter for selectively transmitting visible light and absorbing infrared light on the front surface of an image pickup device and performing photographing in the daytime, and removing the infrared-light cut filter disposed on the front surface of the pickup device and performing photographing with infrared light at night so that night photographing sensitivity increases and night monitoring precision is improved has been proposed.
In a monitoring camera apparatus having such a configuration, an optical path length is different between a case where the photographing is performed using visible light and a case where the photographing is performed using infrared light due to the displacement of the wavelength of light to be used for the photographing by conditions such as the existence of the infrared-light cut filter, and lighting, and the like. For example, there is a problem that if the optical path length is set to an optimal length with respect to the photographing with visible light in the daytime, a photographed image defocuses when the photographing using visible light and infrared light is performed at night.
In order to solve such a problem, for example, a photographing apparatus having a configuration capable of manually adjusting a position of an image pickup device in the optical axis direction if necessary has been practically used. An example of a method for adjusting the position of the image pickup device in the optical axis direction includes a method in which an image pickup device is movably held in the optical axis direction and urged in one direction by an elastic means, and an adjustment ring having a cam mechanism is rotated so as to press the image pickup device in the opposite direction (see, for example, patent document 1).
Furthermore, recently, a monitoring camera apparatus capable of obtaining a sharply focused image at any time of day or night has been proposed, in which when an infrared-light cut filter is disposed on and removed from the optical path, an image pickup device is moved in the optical axis direction to a position having the highest focused value while referring to the focused value of a video signal output from the image pickup device, thereby correcting the difference in the focal length caused by the difference in the optical path length at the time of photographing with visible light and with both visible light and infrared light as mentioned above (see, for example, patent document 2).
In such a monitoring camera apparatus, a lead screw is used for moving the image pickup device, a nut portion rotatably provided to the lead screw is provided, the image pickup device is attached to a chassis whose operation is limited in the optical axis direction by a guide rod, and the lead screw is driven to be rotated by a stepping motor. With such a configuration, by rotating the lead screw by the rotation of the stepping motor, the image pickup device can be moved by a desired distance in the direction of the optical axis of a lens.
However, in the above-mentioned monitoring camera apparatus described in the patent document 2, when the chassis having the image pickup device, which is supported by two axes of the lead screw and the guide rod, moves in the optical axis direction, the image pickup device is moved. Therefore, since it is necessary to provide two axes, the structure becomes larger in the optical axis direction, making it difficult to reduce the size of the apparatus.
Furthermore, as described in the patent document 1, it is thought that an adjustment ring having a cam mechanism is rotated by a motor to control the driving portion to detect a position with the maximum focused value and to be stopped at the position, and thus the position of the image pickup device in the optical axis direction is adjusted. With such a configuration, the problem that the size of the structure is increased in the optical axis direction is solved. However, in general, in the technology described in patent document 1, an urging force of an elastic means for urging the image pickup device to the adjustment ring is designed so that the image pickup device is prevented from moving largely with a small force, that is to say, the torque necessary to rotate the adjustment ring manually is increased. On the other hand, the focused value is detected continuously while the image pickup device is moved in the optical axis and the image pickup device is moved to a position in which the detected value becomes maximum. In order to do so, it is necessary to move the image pickup device smoothly. However, as mentioned above, since the image pickup device is urged with a large force in the direction of the adjustment ring, in order to rotate the adjustment ring, a large motor is needed. Therefore, it is difficult to move the image pickup device smoothly by a small motor with a relatively small driving force.
[Patent Document 1] Japanese Patent Unexamined Publication No. 2000-165733
[Patent Document 2] Japanese Patent Unexamined Publication No. 2003-274229